Micro-fluid ejection heads are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used micro-fluid ejection head is in an ink jet printer. Ink jet printers continue to be improved as the technology for making the micro-fluid ejection heads continues to advance. New techniques are constantly being developed to provide low cost, highly reliable printers which approach the speed and quality of laser printers. An added benefit of ink jet printers is that color images can be produced at a fraction of the cost of laser printers with as good or better quality than laser printers. All of the foregoing benefits exhibited by ink jet printers have also increased the competitiveness of suppliers to provide comparable printers in a more cost efficient manner than their competitors.
One area of improvement in the printers is in the print engine or micro-fluid ejection head itself. This seemingly simple device is a relatively complicated structure containing electrical circuits, ink passageways and a variety of tiny parts assembled with precision to provide a powerful, yet versatile micro-fluid ejection head. The components of the ejection head must cooperate with each other and with a variety of ink formulations to provide the desired print properties. Accordingly, it is important to match the ejection head components to the ink and the duty cycle demanded by the printer. Slight variations in production quality may have a tremendous influence on the product yield and resulting printer performance.
The primary components of a micro-fluid ejection head are a semiconductor substrate, a nozzle plate and a flexible circuit attached to the substrate. The semiconductor substrate is preferably made of silicon and contains various passivation layers, conductive metal layers, resistive layers, insulative layers and protective layers deposited on a device surface thereof. Fluid ejection actuators formed on the device surface may be thermal actuators or piezoelectric actuators. For thermal actuators, individual heater resistors are defined in the resistive layers and each heater resistor corresponds to a nozzle hole in the nozzle plate for heating and ejecting fluid from the ejection head toward a desired substrate or target.
The nozzle plates typically contain hundreds of microscopic nozzle holes for ejecting fluid therefrom. A plurality of nozzle plates are usually fabricated in a polymeric film using laser ablation or other micro-machining techniques. Individual nozzle plates are excised from the film, aligned, and attached to the substrates on a multi-chip wafer using an adhesive so that the nozzle holes align with the heater resistors. The process of forming, aligning, and attaching the nozzle plates to the substrates is a relatively time consuming process and requires specialized equipment.
Fluid chambers and ink feed channels for directing fluid to each of the ejection actuator devices on the semiconductor chip are either formed in the nozzle plate material or in a separate thick film layer. In a center feed design for a top-shooter type micro-fluid ejection head, fluid is supplied to the fluid channels and fluid chambers from a slot or ink via which is formed by chemically etching, dry etching, or grit blasting through the thickness of the semiconductor substrate. The substrate, nozzle plate and flexible circuit assembly is typically bonded to a thermoplastic body using a heat curable and/or radiation curable adhesive to provide a micro-fluid ejection head structure.
In order to decrease the cost and increase the production rate of micro-fluid ejection heads, newer manufacturing techniques using less expensive equipment is desirable. These techniques, however, must be able to produce ejection heads suitable for the increased quality and speed demanded by consumers. As the ejection heads become more complex to meet the increased quality and speed demands of consumers, it becomes more difficult to precisely manufacture parts that meet such demand. Accordingly, there continues to be a need for manufacturing processes and techniques which provide improved micro-fluid ejection head components.
Exemplary embodiments of the disclosure provide a method of making a micro-fluid ejection head structure and micro-fluid ejection heads made by the method. The method includes applying a tantalum oxide layer to a surface of a fluid ejection actuator disposed on a device surface of a substrate so that the tantalum oxide layer is the topmost layer of a plurality of layers including a resistive layer, and a protective layer selected from a passivation layer, a cavitation layer, and a combination of a passivation layer and a cavitation layer. The tantalum oxide layer has a thickness (t) that satisfies an equation t=(¼*W/n), wherein W is a wavelength of radiation from a radiation source, and n is a refractive index of the tantalum oxide layer. A photoimageable layer is also applied to the substrate. The photoimageable layer is imaged with the radiation source and then developed.
Another exemplary embodiment of the disclosure provides a micro-fluid ejection head. The micro-fluid ejection head has a substrate including at least one ejection actuator, wherein the ejection actuator includes a resistive layer, and at least one protective layer selected from a passivation layer and a cavitation layer. A tantalum oxide layer is disposed as a topmost layer of the ejection actuator. The tantalum oxide layer has a thickness (t) as determined by an equation t=(¼*W/n), wherein W is a wavelength of radiation from the radiation source, and n is a refractive index of the tantalum oxide layer. At least one photoimageable layer is disposed on the substrate so that the tantalum oxide layer is disposed between the photoimageable layer and the substrate.
In another embodiment there is provided a method for imaging a photoimageable layer attached to a device side of a substrate having fluid ejection actuators on the device side of the substrate. According to the method, a tantalum oxide layer is applied to an exposed surface of the fluid ejection actuators. The tantalum oxide layer has a thickness sufficient to absorb radiation used to image the photoimageable layer. The fluid ejection actuators include at least one resistive layer and at least one protective layer disposed on the resistive layer. A photoimageable layer is also applied to the device side of the substrate. The photoimageable layer is imaged with a radiation source to provide fluid flow features therein.
An advantage of the embodiments described herein is that they may provide an improved micro-fluid ejection head structures and, in particular, improved nozzle plates and thick film layers for micro-fluid ejection heads. Another advantage is that the methods may enable the formation of nozzle holes, fluid ejection chambers, and fluid flow channels that have precise sizes and shapes. Other advantages of the embodiments described herein may include improved protection of the fluid ejection actuators by the presence of the tantalum oxide layer on an exposed surface of the fluid ejection actuators.